Positive displacement pump



i 1970 I R. J. REEVE ETAL 3, 5105'232 v POSITIVE DISPLACEMENT PUMP Filed Jan. 8, 1968 2 Sheets-Sheet 1 H L F16. '2. 44

/A/l EA/T0ES FP/cHARD J. PEEz/E, 650265 I. NOAH 32 ATTQQA/EY May 1.970 R. J. REEVE AL 3,510,232

PGSITIVE DISPLACEMENT PUMP Filed Jan. 8, 1968 2 Sheets-Sheet z FIG- 6.

M/l/E/VTOES P/cHA RD J REE 1/5, GEORGE I. /VOA/-/ United States Patent 3,510,232 POSITIVE DISPLACEMENT PUMP Richard J. Reeve, 4117 Vecino, and George I. Noah, 545 Rue Royale, both of Covina, Calif. 91722 Filed Jan. 8, 1968, Ser. No. 696,369 Int. Cl. F04b 9/04, 49/08 US. Cl. 417415 4 Claims ABSTRACT OF THE DISCLOSURE A positive displacement pump having a hollow pump body containing a movable pressure wall, such as a piston, which is driven in a reciprocating pumping motion to pump fluid from a reservoir to a receiver in such a way that the pumping stroke of the pressure wall varies inversely and the driving force on the pressure wall varies directly with the discharge fluid pressure of the pump. The pumping stroke approaches zero and the driving force approaches a maximum at a predetermined discharge pressure, whereby the pump maintains this maximum fluid pressure automatically at zero fluid demand. A fluid pressure device, such as a hydraulic rivet setting tool, utilizing the positive displacement pump to furnish pressurized working fluid for an operating cycle which requires the working fluid at relatively high flow rate and low pressure during the initial portion of the cycle and at low flow rate and high pressure during the final portion of the cycle.

BACKGROUND OF THE INVENTION Field of the invention This invention relates generally to pumps and more particularly to a positive displacement pump characterized by a pressure wall which is driven in a reciprocating pumping motion with a stroke which varies inversely and a driving force which varies directly with the discharge pressure of the pump.

Prior art Many fluid pressure operated devices have an operating cycle which requires a working fluid at relatively high flow rate and relatively low pressure during the initial portion of the cycle and at relatively low flow rate and relatively high pressure during the final portion'of the cycle. Such a device, for example, is a hydraulic rivet setting tool of the kind illustrated in Pat. No. 3,255,675. In this type of tool, a relatively large volume of working fluid at relatively low pressure is required to drive the power piston of the tool through the initial portion of its rivet setting stroke. A relatively small volume of working fluid at relatively high pressure is required to drive the piston through the final portion of its stroke.

A variety of pumping systems have been devised to satisfy these requirements. In general, the existing pumping systems for this purpose comprise two separate pumps, to wit, a high volume low pressure pump for delivering the working fluid during the initial portion of the operating cycle and a low volume high pressure pump for delivering the working fluid during the final portion of the cycle. Such dual pump systems, however, are characterized by numerous deficiencies, notably excessive complexity, size and cost, which detract from their usefulness, particularly in relatively small fluid pressure devices, such as the rivet setting tool referred to above and other similar hydraulic tools.

SUMMARY OF THE INVENTION The present invention provides a positive displacement pump of the general class described which avoids the ice above noted and other drawbacks of the existing fluid pumping systems of this kind. In general terms, the present pump is characterized by a hollow pump body containing a movable pressure wall, such as a piston, and means for driving the pressure wall in a reciprocating pumping motion to pump working fluid from a reservoir to a receiver. This driving means is rendered responsive to the discharge pressure of the pump in such a way that the pumping stroke of the pressure wall varies inversely and the driving force on the pressure wall varies directly with the discharge pressure. In the disclosed embodiment of the invention, the pressure wall driving means includes a rotary motor and a motion translating device in the form of a rotary reciprocating cam mechanism operatively connecting the motor shaft and the pressure wall for converting rotary motion of the shaft into reciprocating motion of the pressure wall. This cam mechanism embodies cam and follower members which undergo relative rotation about the axis of reciprocation of the pressure wall when the motor is energized. The cam member has a resilient inclined ramp formation which is traversed by the follower member and causes relative axial reciprocating motion of the members to drive the pressure wall in its reicprocating pumping motion. During these relative motions of the cam and follower members, the discharge fluid pressure of the pump produces a pressure force on the reciprocating pressure wall which causes the follower member to react axially against the cam member with a load proportional to the discharge pressure. The resilient ramp formation of the cam member deflects under this load in such a way that the rise and angle of incline of the formation decrease with increasing discharge pressure. This reduces the pumping stroke of the pressure wall and simultaneously increases the mechanical advantage of the cam mechanism and hence the driving force exerted on the pressure Wall.

The disclosed embodiment of the invention is a hydraulic rivet pulling or setting tool of the kind referred to earlier. In this tool, the pump is utilized to deliver working fluid under pressure to the power cylinder of the tool to drive the power piston through its working cycle. One unique advantage of the invention in this particular applieation resides in the fact that the pump operates automatically to deliver working fluid to the power cylinder at high flow rate and low pressure during the initial portion of the working cycle wherein the resisting force on the power piston is relatively small and at low flow rate and high pressure during the final portion of the cycle wherein the resisting force on the power piston increases to a maximum. When the power piston reaches the end of its stroke, the fluid demand drops to zero. Under these conditions, the resilient ramp formation of the pressure wall reciprocating cam is deflected to a substantially flat condition, such that the stroke of the pressure wall becomes effectively zero. The pump then acts to maintain a predetermined maximum discharge pressure which is less than that which will cause damage to the tool.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a rivet setting tool em- I bodying a positive displacement pump according to the invention;

FIG. 2 is an enlarged longitudinal section 15 through the upper portion of the tool in FIG. 1;

FIG. 3 is an enlarged longitudinal section through the lower portion of the tool in FIG. 1;

FIG. 4 is a section on reduced scale taken on line 44 in FIG. 3;

FIG. 5 is a view similar to FIG. 4 showing the parts in another position of operation;

FIG. 6 is an enlarged section taken on line 66 in FIG. and

FIG. 7 is an enlarged perspective view of the resilient cam embodied in the pump.

DESCRIPTION OF THE PREFERRED EMBODIMENT In general terms, the invention provides a positive dis placement pump 10 having a hollow body 11 containing a pressure wall 12. Pressure wall 12 is sealed to the pump body 11 so as to define with the later a working chamber 14. The pressure wall is movable in reciprocation relative to the pump body to alternately increase and reduce the volume of the working chamber. Each stroke of the pressure wall in a direction to increase the chamber volume is hereinafter referred to as its suction stroke. Each stroke of the pressure wall in a direction to decrease the chamber volume is referred to as its delivery stroke. The pump has inlet means 16 and outlet means 18'. Inlet means 16 communicates the working chamber 14 with a reservoir 20 containing working fluid. Outlet means 18 communicates the Working chamber to a fluid receiver 24. Positioned within the inlet means 16 and outlet means 18 are intake and suction valves 26, 27, respectively. The intake valve 26 opens during each suction stroke of the pressure wall 12 to permit fluid flow from the reservoir 20 to the working chamber 14 and closes during each delivery stroke of the pressure wall to block re-.

verse flow of the working fluid. The discharge valve 27 opens during each delivery stroke of the pressure Wall to permit flow of working fluid from the working chamber 14 to the fluid receiver 24 and closes during each suction stroke of the pressure wall to block reverse flow of fluid. It is now evident, therefore, that reciprocation of the pressure wall 12 is effective to pump working fluid from the reservoir 20 to the fluid receiver 24.

The present invention is concerned primarily with means 28 for driving the pressure wall 12 in its reciprocating pumping motion. According to the invention, the driving means 28 is rendered responsive to the pressure force on the reciprocating pressure wall 12, and hence to the discharge pressure of the pump, in such a way that the pumping stroke of the pressure wall varies inversely and the driving force on the wall varies directly with the discharge pressure. Progressive reduction of the pumping stroke and increase of the driving force with increasing discharge pressure continues until the discharge pressure attains a predetermined magnitude. At this discharge pressure level, the stroke of the pressure wall approaches zero. Thus, the present positive displacement pump is uniquely adapted to deliver working fluid to the receiver 24 at diminishing flow rate and increasing pressure until the maximum discharge pressure is reached. Thereafter, the pump operates to maintain this maximum discharge pressure level.

To these ends, the pressure wall driving means 28 illustrated includes a motor 30, in this instance an electric motor, having a rotary driven shaft 32. Motor shaft 32 is operatively connected to the pressure wall 12 through a motion translating mechanism in the form of a rotary reciprocating cam mechanism 34. This cam mechanism converts rotary motion of the shaft to reciprocating motion of the pressure Wall. The cam mechanism has a cam member 36 engaged by a follower member 38. One of these members is connected to the pressure Wall 12 and the other member is connected to the motor shaft 32 in such a way that the members undergo relative rotation about the axis 40 of reciprocation of the pressure wall during operation of the motor. Cam member 36 has an inclined resilient ramp formation 42 which is transversed by the follower member 38 during relative rotation of the members and imparts relative axial reciprocating motion to the members along the axis 40. This relative reciprocating motion of the cam and follower members drives the pressure wall 12 in its reciprocating pumping motion.

A helical spring 43 exerts force on cam member 36 through the follower member 38. The ramp formation 42 of the cam member deflects under this axial load. This deflection of the ramp formation has the two-fold effect of reducing its rise and reducing its incline angle. The reduction in the rise of the ramp formation reduces the pumping stroke of the pressure wall 12. The reduction in the incline angle of the ramp formation increases its effective mechanical advantage and, thereby, the axial driving force exerted on the pressure wall.

As will become evident from the ensuing description, the present pump may be employed in a wide variety of applications and to deliver fluid to a wide variety of fluid receivers. The particular embodiment of the invention which has been selected for illustration is a hand tool, more specifically a blind rivet pulling or setting tool. This tool has a power cylinder 44 which constitutes the fluid receiver 24 and contains a power piston 46. The piston has a coupling 48 for connection to a rivet stem to be pulled or set. The outlet means 18 of the pump 10 communicates to the power cylinder 44 through a control valve 50. Power cylinder 44 also communicates through the control valve to the working fluid reservoir 20. Embodied in the illustrated rivet setting tool is a switch 52 for controlling the pump motor 30. As will be explained presently, this switch is arranged for operation by both the power piston 46 and the control valve 50.

The illustrated rivet setting tool has a normal inoperative condition illustrated in FIGS. 2 and 3. In this condition, the control valve 50 communicates the pump outlet means 1 8 and the working fluid reservoir 20 to the power cylinder 44 at the rear and front sides, respectively, of the power piston 46. The piston occupies its illustrated forward or extended position, and the motor switch 52 is open, whereby the pump motor 30 is de-energized. The tool is conditioned for a rivet setting operation by attaching the piston coupling 48 to a rivet stem to be pulled. At this point, the control valve 50 is actuated to communicate the pump outlet means 18 and the reservoir 20 to the power cylinder 44'at the front and rear sides, respectively, of the power piston 46. This actuation of the control valve also closes the motor switch 52 to energize the pump motor 30. The motor then drives the pressure wall 12 in its reciprocating pumping motion through the rotary reciprocating cam mechanism 34. Under these conditions, working fluid is pumped from the reservoir 20 to the power cylinder 44 in front of the power piston 46 so as to drive the piston rearwardly in the cylinder. Initially, the resistance to rearward retraction of the power piston is relatively small. Under these conditions, the ramp formation 42 of the pressure wall reciprocating cam 36 remains relatively undeflected, whereby the cam mechanism drives the pressure wall 12 to its maximum stroke with minimum driving force. The pump 10 thus delivers working fluid to the power cylinder 44 at maximum flow rate and minimum pressure. As the rearward rivet setting stroke of the power piston 46 continues, the resistance to rearward retraction of the piston increases. This increases the back pressure on the pump and hence the fluid pressure force on the power piston 12. The cam ramp formation 42 is thereby deflected to progressively reduce the pumping stroke of the pressure wall 12 and progressively increase the driving force on the wall. As a result, the pump 10 delivers working fluid to the power cylinder 44 at gradually reducing flow rate and gradually increasing pressure. When the power piston 46 reaches the rear end of its setting stroke, the fluid demand drops to zero. Under these conditions, the back pressure on and hence the discharge pressure of the pump rises to a level which finally deflects the cam ramp formation 42 to its generally flat condition. The pumping stroke of the pressure wall 12 then becomes substantially zero, and the pump operates to maintain a predetermined discharge pressure. It will be understood that during this retraction stroke of the power piston 46,

the working fluid behind the piston is displaced from the power cylinder 44, through the control valve 50, to the reservoir 20.

At the conclusion of the rearward rivet setting stroke of the power piston 46, the control valve 50 is released for return to its normal position of FIG. 2. The motor switch 52, however, remains locked in its closed position by the currently retracted power piston 46. Accordingly, high pressure fluid from the pump is delivered to the power cylinder 44 at the rear side of the piston to extend the latter forwardly. Working fluid is now displaced from the front side of the piston to the reservoir through the control valve 50. As the piston returns forwardly, the back pressure on the pump gradually drops and the cam ramp formation 42 returns to its normal undeflected condition. Thus, the discharge flow rate of the pump increases and the discharge pressure of the pump decreases. Upon final return of the piston to its forward position, it releases the motor switch 52 which then reopens to de-energize the pump motor 30 and complete one operating cycle of the tool.

Referring now in greater detail to the drawings, the pump body 11 comprises a generally tubular casting having end faces 54 and 56. The housing 58 of the pump motor 30 is bolted to the lower end of the pump body 11 with the upper wall 60 of the housing seating against the lower body face 54. The motor axis coincides with the reciprocation axis 40 of the pressure wall 12. The power cylinder 44 is bolted to the upper end of the pump body 11 with a lower face 62 of the cylinder seating against the upper body face 56. Entering the lower end and extending upwardly through the pump body 11 on the reciprocation axis 40 is a cylinder 64. Threaded or otherwise fixed within the lower end of this cylinder is a barrel 66. Barrel 66 has upper and lower generally tubular parts 68 and 70 which are threadedly joined to one another and sealed to the cylinder wall by the illustrated O-rings. These barrel parts are shaped to define therebetween the working chamber 14. Extending axially through the lower barrel parts 70 is a main pump cylinder 74. This cylinder opens upwardly to the working chamber 14 and downwardly to the lower end of the lower barrel part. Pump cylinder 74 contains the pressure wall 12, which, in this instance, is a rod shaped piston slidably fitted within and extending from the lower end of the pump cylinder. The lower end of the lower barrel part 70 extends through an opening in the upper wall 60 of the motor housing 58 and has a flange 76 which seats against the under side of the wall. Bolts 78 extend through a cap 80 on the lower end of the lower barrel part 70, through the housing wall 60, and are threaded in pump body 11 to join the pump body and the motor housing 58. The piston 12 is sealed to the barrel 66 by an O-ring which is captivated between the lower barrel part 70 and the cap 80.

Entering the lower end of an extending upwardly through the pump body 11 in spaced parallel relation to the body cylinder 64 is a cylinder 82. The lower end of cylinder 82 is closed by a pair of closure discs 84, 86 which are disposed one on top of the other and are sealed by the illustrated O-rings to the cylinder wall. The lower disc 84 seats against the upper wall 60 of the motor housing 58. The upper disc 86 is retained against axial movement by a snap ring 88 seating within a groove in the wall of the cylinder 82. The cylinder space above the upper closure disc 86 forms the working fluid reservoir 20. Slidable within the upper end of this reservoir is a piston 90 which is urged downwardly in the reservoir by a spring 92.

As noted earlier, the pump 11 of the illustrated rivet setting tool has inlet means 16 communicating the reservoir 20 to the working chamber 14 and outlet means 18 communicating the working chamber to the fluid receiver 24. Inlet means 16 includes a cavity 94 which is formed in the upper face of the lower reservoir closure disc 84 and communicates to the reservoir 20 proper through a port 96 in the upper closure disc 86. Leading laterally from the cavity 94 is a passage 98 which opens to the pump body cylinder 64 and communicates to the working chamber 14 through an external circumferential recess 100 in the lower barrel part 70 and a port 102 in the upper barral part 68. The outlet means 18 includes a port 104 in the upper barrel part 68 which communicates the working chamber 14 to the body cylinder 64 above the barrel 66. Leading from the upper end of the cylinder 64 is an outlet passage 106 which opens at its upper end to a valve chamber 108 containing the control valve 50. It will also be recalled that the pump 11 has intake and discharge valve means 26, 27 for controlling fluid flow to and from the working chamber 14. In this instance, the intake valve 26 is a check valve in the form of a resilient flapper which is bolted to the under face of the upper reservoir closure disc 86 and is biased upwardly into seating contact with the face. Similarly, the discharge valve 27 is a check valve in the form of a resilient flapper which is bolted to the upper end face of the pump barrel 66. The discharge valve is biased downwardly into seating engagement with the upper barrel face. It is evident that the intake valve 26 opens to permit fluid flow from the reservoir 20 to the working chamber 14 and closes to block reverse flow of the fluid. The discharge valve 27 opens to permit fluid flow from the working chamber 14 to the control valve chamber 108 and closes to block reverse flow of the fluid.

Turning now to the cam mechanism 34 which operatively connects the pump motor shaft 32 to the pump piston 12, it will be observed that the cam member 36 is carried by a circular plate 110 rigidly fixed to the upper end of the shaft. This plate has an upper raised annular shoulder 112 which is radially slotted at diametrically opposite locations 114. Hardened steel wear plates 116 are placed in the bottoms of the slots 114 and are secured in position by screws, as shown. Concentrically positioned atop of and bolted to the plate shoulder 112 is a retaining ring 118 having an inner beveled face 120. Cam 36 is fashioned from spring steel or other suitable spring metal and has the shape best illustrated in FIG. 7. The cam includes a generally circular central portion 122 and cams 124 extending from diametrically opposite sides of the central portion. The central cam portion 122 is folded into a generally V-shape about a diameter extending normal to the common longitudinal axis of the cam tabs 124. This folded central cam portion defines the ramp formation 42 of the cam. Referring particularly to FIGS. 36, it will be observed that the cam 36 is dimensioned to be positioned on its supporting plate 110 in such a way that the central cam portion 122 fits, with a small radial clearance, within the circular recess defined and bounded by the upstanding plate shoulder 112. The cam tabs 124 fit closely within the shoulder slots 114. The cam is placed in such a way that its ramp formation 42 projects upwardly toward the pump piston 12.

The follower member 38 of the cam mechanism 34 comprises a cross head 126 which is threadedly joined to and extends transversely of the lower end of the pump piston 12. The spring 43 is disposed about cross head 126 and cap 80, and engages the housing 60 to urge cam follower 38 against cam 36. Extending through the cross head, normal to the axis of the piston, is an axle 128 on the ends of which are mounted follower Wheels 130. These wheels bear on the upper surface of the central cam portion 122, that is the upper surface of the cam ramp formation 42. Extending between the pump body 11 and the cross head 126 are pins 132 which are fixed in one of these parts and slide within bores in the other part. Pins 132 thus restrain the cam follower 38 against rotation relative to the pump body 11 while permitting the follower to reciprocate axially relative to the body with the piston 12. It is evident at this point that assuming the cam follower 38 is urged downwardly into seating engagement with a cam 36 by the action of the spring 43 on the piston 12, energizing of the pump motor 30 is effective to drive the cam in rotation relative to the follower. During this rotation of the cam, the cam follower rollers 130 ride back and forth across the cam ramp formation 42 so that this ramp formation imparts an axial reciprocating motion to the pump piston 12. It is significant to note here that the fluid pressure force on the piston loads the ramp formation in a downward direction in FIG. 3 and tends to deflect this ramp formation from its normal unstressed condition of FIG. 3 to its generally flat condition of FIG. 6.

The pump control valve 50 includes a plunger 134 which slides in a bore 136 extending through the pump body 11 transversely of its cylinders 64, 82. Plunger bore 136 intersects the valve chamber 108. The inner end of the bore opens to a longitudinal passage 138 in the pump body 11 through which extend energizing leads 140 for the pump motor 30. These leads connect to the motor switch 52 which is positioned within the upper end of the passage 138 opposite the rear end of the control valve plunger 134. The valve plunger is urged to the left in FIG. 2 by a leaf spring 141 which is positioned within the passage 138 and secured to the pump body 11. A trigger 142 pivoted on the pump body engages the outer or left-hand end of the valve plunger 134 in such a way that the plunger may be retracted to the right in FIG. 2, against the action of the plunger spring 141, by depression of the trigger. Plunger 134 operates a slide valve 144 similar to that disclosed in the aforementioned Pat. No. 3,255,675. Accordingly, it is unnecessary to describe the slide valve in detail. Suflice it v to say that in its normal position of FIG. 2, the slide valve 144 communicates the pump discharge passage 106 to the power cylinder 44 at the rear side of the power piston 46 through a passage 146 in the cylinder wall. In this position, the slide valve also communicates the fluid reservoir 20 to the power cylinder at the front side of the power piston through a passage 148 in the power cylinder wall. Retraction of the control valve plunger 134 to the right in FIG. 2. communicates the pump discharge passage 106 to the power cylinder passage 148 and the reservoir 20 to the power cylinder passage 146. As the plunger approaches its fully retracted position, it engages and closes the motor switch 52. The illustrated O-rings on the valve plunger seal the latter to the wall of its containing bore 136, at opposite sides of the valve chamber 108.

The power piston 46 is fixed to a rod 152. The front end of this rod extends from the front end of the power cylinder '44 and mounts the rivet stem coupling 48. This end of the rod is slidably supported in and sealed to the front end wall of the power cylinder. The rear end of the piston rod extends through and is slidably supported in and sealed to a disc 154 positioned within the power cylinder. This disc is axially positioned between an internal shoulder and a snap ring within the cylinder. Mounted for lateral floating movement within the power cylinder 44, rearwardly of the piston rod bearing disc 154, is a switch actuating cup 156 having a tubular collar 158 surrounded at its rear end by an annular flange 160. The edge of this flange seats against a pin 162 mounting at its lower end a beveled motor switch actuator 164. This actuator engages the forward contact of the motor switch 52 which urges the actuator to its position of FIG. 2, wherein the central opening in the collar 158 is eccentric to the piston rod 152. The rear end of the piston rod is beveled, as shown, so that it may enter the collar 158 during initial rearward retraction of the power piston. As the piston rod enters the collar, it cams the latter downwardly to a position wherein the motor switch actuator 164 engages and closes the contacts of the motor switch 52.

The operation of the illustrated rivet setting tool is obvious from the preceding description. Thus, when the tool is in its normal inoperative condition illustrated in FIGS. 2 and 3, the control valve plunger 134 is extended to its forward position by the plunger spring 141. In this position, the slide valve 144 is positioned to communicate the pump discharge passage 106 to the rear side of the power piston 46 and the reservoir 20 to the front side of the piston. The motor switch 52 is open so that the pump motor 30 is de-energized. The tool is caused to proceed through its operating cycle by depressing the control valve trigger 142 to retract the control valve plunger 134 to the right in FIG. 2. This retraction of the plunger shifts the slide valve 144 rearwardly to communicate the pump discharge passage 106 to the front side of the power piston 46 and the reservoir 20 to the rear side of the piston. Simultaneously, the control valve plunger 134 closes the motor switch 52 to energize the pump motor 30. The cam 36 is then driven in rotation relative to the cam follower 38, thus imparting a reciprocating pumping motion to the pump plunger 12. Working fluid is then pumped from the reservoir 20, through the working chamber 14, to the power cylinder 44 at the front side of the power piston 46 to cause rearward retraction of the piston. During initial retraction of the piston, the switch cup 156 is shifted laterally to lock the motor switch 52 in its closed condition. During this rearward retraction of the power piston, the resistance imposed on the piston by the rivet being set increases, thus creating an increasing back pressure on the pump 10. This increasing back pressure reacts on the cam 36, through the pump piston 12 and cam rollers 130, and causes gradual deflection of the cam ramp formation 42 from its normal unstressed condition of FIG. 3 to its generally flattened condition of FIG. 6. Both the rise and the angle of the ramp formation are thereby decreased to reduce the pumping stroke of the piston 12 and increase the driving force on the piston. Thus, the rate of delivery of the working fluid to the power cylinder 44 is gradually reduced and the dis charge pressure of the pump is gradually increased. When the power piston 46 finally reaches the end of its retracted stroke, the fluid demand drops to zero, and the cam ramp formation 42 is finally deflected to its generally flattened condition of FIG. 6. Under these conditions, the pump 11 operates to maintain a predetermined maximum discharge pressure which may be regulated by varying the stiffness of the cam 36.

Return of the power piston 44 to its forward position of FIG. 2 is accomplished by releasing the control valve trigger 142. This permits return of the control valve plunger 134 to its forward position under the action of the plunger spring 141. The slide valve 144 is then repositioned to communicate the pump discharge passage 106 to the rear side of the power piston 44 and the reservoir 20 to the front side of the piston. It will be recalled that the motor switch 52 is currently locked in its closed position by the currently retracted power piston. Accordingly, the pump motor 30 remains energized. Under these conditions, the high pressure fluid from the pump is delivered to the rear side of the power piston 46 to extend the latter forwardly. During this return stroke of the power piston, the fluid pressure induced load on the cam 36 diminishes with the result that its ramp formation 42 gradually returns to its unstressed condition of FIG. 3. Thus, the pumping stroke of the piston 12 is gradually increased and the driving force on the piston is gradually reduced during the return stroke of the power piston. Final return of the piston to its position of FIG. 2 releases the motor switch actuating cup 156 for upward movement to its normal position of FIG. 2. In this position, the motor switch 52 reopens to de-energize the pump motor 30 and complete the operating cycle of the tool.

The inventors claim:

1. A positive displacement pump comprising:

a hollow pump body,

a movable pressure wall within and sealed to said body and defining with said body a working chamber,

said pressure wall being movable with a reciprocating motion relative to said body to alternately increase and reduce the effective volume of said chamber,

each stroke of said pressure wall in a direction to increase said chamber volume constituting a suction stroke, and each stroke of said pressure wall m a direction to reduce said chamber volume constituting a delivery stroke,

said pump having an inlet passage to said chamber adapted for communication to a source of working fluid and an outlet passage from said chamber adapted for communication to a fluid receiver,

valve means for controlling flow through said passage, whereby reciprocating motion of said pressure wall is effective to pump working fluid from said inlet passage through said working chamber to said outlet passage, and

means responsive to the discharge pressure 1n sa 1d outlet passage for driving said pressure wall 1n ts reciprocating motion with a stroke which varies inversely with said discharge pressure, said driving means comprising a motor having a rotary driven shaft, and a motion translating mechanism operatively connecting said shaft and pressure wall and responsive to the fluid pressure force on said wall for converting the rotary motion of said shaft to reciprocating motion of said pressure wall with a stroke which varies inversely with said discharge pressure, said motor translating means comprising a cam chamber, a follower member engaging said cam member, means operatively connecting said members to said pressure wall and motor shaft, respectively, whereby during rotation of said shaft said members undergo relative rotation about the axis of reciprocation of said wall, and said follower member exerts an axial load on said cam member proportional to said fluid pressure force, and said cam member has a resilient ramp formation which imparts a relative axial reciprocating motion to said members along said axis during said relative rotation of said members and is deflected by said load to reduce the rise of said ramp formation and thereby the stroke of said pressure wall as said load increases.

2. A positive displacement pump comprising:

a hollow pump body, a movable pressure wall within and sealed to said body and defining with said body a working chamber, said pressure Wall being movable with a reciprocating motion relative to said body to alternately increase and reduce the effective volume of said chamber,

each stroke of said pressure wall in a direction to increase said chamber volume constituting a suction stroke, and each stroke of said pressure wall in a direction to reduce said chamber volume constituting a delivery stroke,

said pump having an inlet passage to said chamber adapted for communication to a source of working fluid and an outlet passage from said chamber adapted for communication to a fluid receiver,

valve means for controlling flow through said passage, whereby reciprocating motion of said pressure wall is effective to pump working fluid from said inlet passage through said working chamber to said oultet passage, and

means responsive to the discharge pressure in said outlet passage for driving said pressure wall in its reciprocating motion with a driving force during each delivery stroke which varies directly with said discharge pressure, said driving means comprising a motor having a rotary driven shaft, and a motion translating mechanism operatively connecting said shaft and pressure wall and responsive to the fluid pressure force on said pressure wall for converting the rotary motion of said shaft to reciprocating motion of said pressure wall with a driving force on said wall which varies directly with said discharge pressure, said motor translating means comprising a cam member, a follower member engaging said cam member, means operatively connecting said members to said pressure wall and motor shaft, respectively, whereby rotation of said shaft drives said members in relative rotation about the axis of reciprocation of said pressure wall and said follower member exerts an axial load on said cam member proportional to said force, and said cam member has a resilient inclined ramp formation which imparts a relative axial reciprocating motion to said members along said axis during said relative rotation of said members and deflects under said load to reduce the angle of said ramp formation and thereby increase the driving force on said pressure wall as said load increases. 3. A positive displacement pump comprising: a hollow pump body,

a movable pressure wall within and sealed to said body and defining with said body a working chamber, said pressure wall being movable with a reciprocating motion relative to said body to alternately increase and reduce the effective volume of said chamber,

each stroke of said pressure wall in a direction to increase said chamber volume constituting a suction stroke, and each stroke of said pressure wall in a direction to reduce said chamber volume constituting a delivery stroke,

said pump having an inlet passage to said chamber adapted for communication to a source of working fluid and an outlet passage from said chamber adapted for communication to a fluid receiver,

valve means for controlling flow through said passage, whereby reciprocating motion of said pressure wall is effective to pump working fluid from said inlet passage through said working chamber to said outlet passage, and

means responsive to the discharge pressure in said outlet passage for driving said pressure wall in its reciprocating motion with a stroke which varies inversely with said discharge pressure and a driving force during each delivery stroke which varies directly with said discharge pressure, said driving means comprising a motor having a rotary driven shaft, and a motion translating mechanism operatively connecting said shaft and pressure wall and responsive to the fluid pressure force on said wall for converting the rotary motion of said shaft to reciprocating motion of said pressure wall with a stroke which varies inversely with said discharge pressure and a driving force on said wall which varies directly with said discharge pressure, said motor translating means comprising a cam member, a follower member engaging said cam member, means operatively connecting said members to said pressure wall and motor shaft, respectively, whereby rotation of said shaft drives said members in relative rotation about the axis of reciprocation of said pressure wall and said follower member exerts an axial load on said cam member proportional to said force, and said cam member has a resilient inclined ramp formation which imparts a relative axial reciprocating motion to said members along said axis during said relative rotation of said members and deflects under said load to reduce the rise and angle of said ramp formation, thereby to reduce the stroke of said pressure wall and increase the driving force on said pressure wall as said load increases.

-1 1 1 2 4. A pump according to claim 3 wherein: 3,164,024 1/ 1965 Tarry et a1. said pressure wall is a piston movable within a cylin- 3,301,195 1/ 1967 Streeter 103150 der 1n sald pump body. FOREIGN PATENTS References Cited 5 284,380 1/1928 Great Britain. UNITED STATES PATENTS WILLIAM L. FREEH, Primary Examiner 1,548,043 8/1925 Kennedy 745'68 2,367,545 1/ 1945 Udale 10338 US. Cl. X.R. 2,550,392 4/1951 Venning 103-211 2,604,054 7/1952 Fitch 10*3--38 10 60 74568 92 169 

